The "TouchStart" event is a feature in web development that detects when a user touches a touchscreen device. It is part of the Touch Events API, which allows developers to create interactive applications for devices like smartphones and tablets. This event is triggered when a finger first makes contact with the screen, enabling responsive actions in applications. When the TouchStart event occurs, it can be used to initiate various functions, such as starting a drag-and-drop action or opening a menu. This event is essential for enhancing user experience on touch-enabled devices, making interactions smoother and more intuitive.